4,4′-Dichlorodiphenylsulfone, abbreviated as DCDPS, is an organic sulfone with the formula (ClC6H4)2SO2. It is most commonly used as a key monomer in the manufacture of sulfone polymers.
Other dihalodiarylsulfones than 4,4′-dichlorodiphenylsulfone and related derivatives are also of great industrial importance. Mention can be made, inter alia, of 4,4′-bis-(4-chlorophenylsulfonyl)biphenyl or of 4,4′-bis-(4-chlorophenylsulfonyl)terphenyl.
High purity levels are required in order to produce high quality polymers. More particularly, high isomeric purity is required; typical isomeric purity requirements are 98.4% and higher. Different processes for manufacturing dihalodiarylsulfones are known. In general, they result in different regioselectivity levels, but most of the time the intrinsic regioselectivity is lower than the final required purity. Hence, a waste stream consisting of dihalodiarylsulfone isomers is created. This waste stream contains unwanted isomers produced in the process but also some of the desired isomer lost during the purification step. The amount of this waste stream and its composition depend on the synthetic route chosen but also on the purification scheme used.
In particular, DCDPS is generally prepared by a two-step Friedel-Crafts sulfonation and sulfonylation reaction.
U.S. Pat. No. 4,983,773 discloses the synthesis of DCDPS by treating chlorobenzene with sulfuric acid at a temperature of 200-250° C., according to the following equations:Cl-Ph+H2SO4→Cl-Ph-SO3H+H2OCl-Ph+Cl-Ph-SO3H→Cl-Ph-SO2-Ph-Cl+H2O.
The reaction goes to completion in approximately 10 hours and produces a high yield of 4,4′-dichlorodiphenyl sulfone. The reaction can be carried out in the presence of boric acid or trifluoromethanesulfonic acid, which increases the DCDPS yield by reducing the formation of the 2,4′- and 3,4′-isomers. However, the use of high temperature leads to a decrease in selectivity (80-87% of the 4,4′-isomer).
U.S. Pat. No. 3,855,312 discloses a process for manufacturing 4,4′-dichlorophenylsulfone which comprises reacting chlorobenzene with sulfur trioxide in sulfuric acid to obtain a reaction mixture containing 4-chlorobenzenesulfonic acid, which is subsequently reacted with chlorobenzene at high temperature and superatmospheric pressure. The reaction product consists in a mixture containing 4,4′-dichlorophenylsulfone and its 2,4′- and 3,4′-isomers.
The formation of undesired disulfone isomers represents a loss in yield with the cost associated with the raw materials consumed to prepare these isomers. As opposed to sulfonylphenol-type of monomers, such as 4,4′-sulfonyldiphenol, dihalodiarylsulfone isomers cannot be chemically converted into the desired isomer in a simple one-step isomerization.
Therefore, there remains a need for reducing yield loss in manufacturing processes of dihalodiarylsulfones and possibly producing useful intermediates from the above-mentioned waste streams of unwanted isomers.